Saw chains having chisel-type cutter links, that is cutter links in which the top plate portion and the side slitter portion form a sharp angle, and, therefore, a sharp corner at the juncture of the top cutting edge and the side cutting edge, are very effective. However, they require expertise in sharpening and are not nearly so widely used as saw chains of the chipper-type which have a rounded corner formed by the top cutting edge and the side cutting edge, the rounded corner being less adapted to slitting than the sharp corner of the chisel-type teeth but being sharpenable without the great skill required by the chisel teeth. In each of Silvon U.S. Pat. Nos. 3,263,717 and 3,469,610, Oehrli U.S. Pat. No. 3,260,287 and Frederickson U.S. Pat. No. 3,189,064, there is disclosed a tooth adapted to have its top cutting edge sharpened uniformly with little skill required but the side slitter edge must be hand filed and this tooth does not present an easily maintained sharp corner. Neumeier U.S. Pat. No. 3,581,785 also shows top cutting teeth which can be sharpened easily but which have no side slitter portions. Dolata et al U.S. Pat. Nos. B 3,921,490 and 4,023,453 disclose a saw chain having a twisted tooth which can be top sharpened and a side slitter which can be sharpened at the outside edge. However, both the top edge and the side slitting edge must include such large angles that they are not good cutters and a sharp corner is not provided. Also, such teeth break off easily.
Most top cutting edges can be sharpened employing an abrasive stone mounted adjacent the drive sprocket of a chain saw and movable radially inwardly against the chain, one example being illustrated in the aforementioned Oehrli U.S. Pat. No. 3,260,287. A grinding stone or the like can also be made elongated and arcuate whereby plural top cutting edges are sharpened as the chain passes around the sprocket, for example as illustrated in the aforementioned Dolata patents, in Carter U.S. Pat. No. 3,457,969, Silvon U.S. Pat. Nos. 3,435,860, 3,487,591 and 3,516,459, Condon et al U.S. Pat. No. 3,526,156 and Van Ourkerk U.S. Pat. No. 3,534,638. These devices are rather complex and expensive, and furthermore the sharpening stone is subject to wear and damage. Graversen U.S. Pat. No. 3,529,495 and Stihl et al U.S. Pat. No. 3,603,179 disclose curved backing plates or the like which support abrasive strip material adjacent the path of the cutter teeth. However, these devices tend to produce rapid wear or damage in the strip material when the same is urged toward the moving saw chain.
Also, the prior art does not disclose a satisfactory device for automatically sharpening cutter teeth with outer side sharpenable surfaces. Although Dolata U.S. Pat. No. 4,023,453 discloses sharpening a rounded corner, no means is disclosed for sharpening an outer side cutting edge of a chisel-type tooth having a sharp corner at the juncture of the side cutting edge and a top cutting edge.